This invention relates to booster rockets, and in particular to the mounting structure by which a booster rocket is secured to the side of a launch vehicle to transmit the thrust of the booster rocket to the launch vehicle.
Launch vehicles for placing commercial and government satellites in orbit and for missions carrying heavy payloads in general are typically equipped with booster rockets to provide the initial thrust to overcome the weight of the payload or the large initial amount of fuel in the vehicle itself and to get the vehicle up to speed. One or more booster rockets are attached to the outer surface of the vehicle, and the attachment is achieved through an attachment structure that transmits the thrust from the booster rocket to the core vehicle, preferably without adding excessive weight to the rocket and vehicle. One type of attachment structure is a metal band that encircles the rocket, and the resulting rocket is known as a strap-on rocket. An alternative is a bolt-on structure, which is an external lug fitting secured by a bolt passing through the rocket motor case and into a load reaction plate located in the rocket interior. Another alternative is a wound-on structure, in which the motor case is filament-wound with a filament impregnated with resin that is cured after winding, and the lug is secured to the motor case by passing windings of the resin-impregnated filament through or over the lug and curing the resin once the windings are in place.
The attachment structure is commonly referred to as a xe2x80x9claunch lugxe2x80x9d or a xe2x80x9cthrust block,xe2x80x9d and to transmit the thrust and carry the weight of the vehicle, the structure must be secure enough to withstand the stresses that are encountered during takeoff. These stresses arise both from the thrust of the booster rocket and from the expansion of the rocket caused by the increase in temperature and pressure as the rocket is being fired. Expansion of the rocket motor imposes shear forces on the bolts or other connections that are part of the attachment structure, placing the integrity of the attachment at risk. Disengagement of the booster rocket during firing results in a loss of thrust to the launch vehicle. Loosening of the attachment may cause the direction of thrust to deviate from the vehicle axis. A similar result may occur if one booster rocket becomes disengaged or loose while the others remain secure.
These and other considerations arising in connection with the attachment of a booster rocket to a launch vehicle are addressed by the present invention, which resides in a mounting structure in the form of a central support plate or hub to which a thrust pin is mounted, a series of struts extending longitudinally from one end of the plate, and a pair of struts extending laterally from the two sides of the plate. Each strut terminates in a base plate, referred to herein as a xe2x80x9cfoot,xe2x80x9d for attachment to the rocket motor case, and the struts are angled relative to the feet to raise the support plate so that the plate will not be in contact with the motor case surface when the feet are secured to the surface. The feet are joined only through the struts, leaving the feet free to spread apart or otherwise move relative to each other to accommodate stress forces exerted on the structure as the rocket motor case expands.
The mounting structure is attached to the rocket motor case with the longitudinal struts extending in the aft direction and the lateral struts (also referred to herein as xe2x80x9ctransversexe2x80x9d struts) extending in directions substantially perpendicular to the axis of the rocket motor. The combination of longitudinal and transverse struts and a raised support plate permits the attachment structure to expand in two directions independently, i.e., axially and circumferentially, and thereby accommodate stress forces in either direction or in both directions simultaneously. The raised central support plate and the angle formed by the two transverse struts provide the structure with the ability to accommodate circumferential expansion by allowing the angle between the struts to increase as the case circumference expands. The transverse struts are also sufficiently wide that the feeT at the ends of these struts are far apart from each other. The stress on the bolts securing the feet to the motor case will then be primarily, and in some cases entirely, a shear stress. Longitudinal expansion is accommodated by the ability of the transverse struts to move longitudinally relative to the central support plate, thereby varying the distance between the feet on the transverse struts from those on the longitudinal struts.
Other features, embodiments, and advantages of the invention will be understood from the description that follows.